Although highly unlikely, it is postulated that single or multiple component failures can result in an uncontrolled high thrust condition. Such a condition may include the actual engine thrust increasing to significantly higher levels than what is being commanded and/or remaining high when low thrust is commanded. For example, though highly unlikely, it is postulated that if the means of metering fuel to the engine (e.g., the fuel metering valve) were to fail in a fixed position, then the pilot may lose the ability to control engine thrust via the thrust/power/throttle levers or the auto-throttle. If the fuel metering means were to fail at the maximum fuel flow position, then engine thrust will continue to increase until either an engine limit is reached or the pilot initiates an intervening action. The engine limit may be, for example, an engine control limit, such as an overspeed protective system, or an inherent limit, such as an engine stall. Intervening actions may include, for example, manually shutting down the affected engine.
Presently, most regulatory bodies address the postulated uncontrolled high thrust condition by relying on crew intervention. That is, it is presently asserted that a flight crew will readily recognize the condition and manually shutdown the affected engine. Engineering studies and service experience indicate that this assertion is not always valid. Moreover, as may be appreciated, even if a flight crew were to recognize the postulated uncontrolled high thrust condition and thus shut down the affected engine, that engine is now unavailable to provide electrical, hydraulic, and/or pneumatic power to the aircraft.
Hence, there is a need for a system and method for detecting an uncontrolled high thrust condition in turbofan gas turbine engines that does not rely, at least solely, on flight crew recognition. The present invention addresses at least this need.